In article <017201c85925$95d70d60$6501a8c0@turtle> you write:
>The XML specification does not actually say what processors should do when
>they encounter a name that is "reserved for standardization", but the
>consensus is that it is not an error to use such a name and therefore they
>should at most give a warning.
The Namespaces spec is a bit more explicit about this. For prefixes
beginning "xml" is says:
* users SHOULD NOT use them except as defined by later specifications
* processors MUST NOT treat them as fatal errors.
There's always the risk that a processor might ignore something that a
newer specification has declared that it should interpret, but the
idea is to ensure that low-level components don't reject documents
because they contain new features that a higher-level component will
be able to interpret.
An XML 1.0 processor that rejected xmlns attributes because they were
reserved would not have been usable with a namespace processing layer,
and a namespace-aware processor that rejected xml:id attributes would
not have been usable with an xml:id layer.
-- Richard